Blend the mayonnaise and lemon juice together. Mix with the diced chicken and celery. Salt to taste and stir in the almonds. Peel the avocados and cut in half lengthwise. On each salad plate, place two lettuce leaves with one avocado half on top. Spoon one-fourth of the chicken salad into the hollow of each avocado half, letting some spill over onto the lettuce.